Wide range ultrahigh frequency tuning cavity



Oct. 7, 1952 H. E. s. STOCKMAN WIDE RANGE ULTRAHIGH FREQUENCY TUNING CAVITY 2 SHEETS SHEET 1 Filed June 25, 1950 III r-lll H. E. s. STOCKMAN WIDE RANGE ULTRAHIGH FREQUENCY TUNING CAVITY Filed June 23, 1950 Oct. '7, 1952 2 SHEETS-SHEET 2 V T MN M F. TH m m N Na T 5 a? WWW Y a My frequency tuning devices.

Patented Oct. 7, 1952 UNITED STATES KVIDE" ULTRAHIG'H FREQUENCY T TUNING CAVITY Harry Ens- 8130911111311, Waltham, Mass.

Application June23, 1950, Serial No. 16.9;9'51

(Granted under the act of March 3, 1883,1115 amended April '30, 1928; 370 O. 'G. =757) '7 Claims.

Theinventiondescribed herein may bemanu-' iactured and used by orior the United States Government for governmental purposes without payment to me Ota 'lyrOyalty thereon.

This invention relates to wide range ultra high It is the object of the invention to provide-a .continuously tunable resonant devicezfor useprincipally in the 300xmegacycle to 3000 megacycle frequency band, butalso useful at frequencies considerably below and above this hand, and tunable over a-frequency rangeof the orderof 1'27. Itis a further object of the invention toprovide a tuner having a high and relatively constant Q, low radiation so that shielding is not required, and freedomirom slidc contacts nde qh g d ices.

.In accordance with the invention the tuner comprisesv a resonant cavity having one or more charge storing gaps and :a movable conductor which may be movedirom a position ,inside the gap for-gaps to ;a position totally outside the gaps. The cavity and movable-conductor are also so arranged that asthe conductor is moved away :from its :positiondnside the gaps it .increasingly restricts th area through which the magnetic field lines pass thus reducing the inductance simultaneously withthe reduction in capacitance of the .gaps resulting from the effective increase ingap spacing. This simultaneous variation of inductance and capacitance makes possible awider tuning range than can be achieved by variationof either alone.

,For a. more complete description of the inventionreference is made to the specific embodimen'ts thereof -shown in the accompanying draw ings inwhich,

Fig. "l is a plan "view of one form of tunable resonant cavity constructed in accordance "with the invention;

Fig. '2 is asectional view-of Fig. l-taken at ,the plane 2---2';

*Fig. -'3 'shows a *modificationof Figs. 1 and -2;

Fig. 4 is-a plan view of anotherembodiment of the invention;

Fig. 5 is a sectional view of Fig. 4 taken at planed-'5;

Fig. "6 showsa third embodiment of a resonator in accordance with the invention; and

Fig; Us a sectional view of Fig. Gtaken at the plane l-'l.

R in t Fig. .1 end? the resonant cavity is boundedfby anenclosure I. Theenclosureis made of ,a' highly conductive metalsuchas brass or copper .and, if .jdesired, the. inner surfaces thereoimaybe plated Witha metal of sti l-higher conductivity such, for exampleyas silver 'in-order to reduce the losses at high frequencies to a minimum. Cylindrical conductors :2 and-3 extend joined by a bridge 8 which is attached to shaft- 9. The cylindrical conductors are made of highly conductive metal, platedif desired, as in the case of the cavity enclosure. be made hollow if desired to save metal and lighten the structure. The bridge limay be made of insulatingmaterial, as in Fig. .2, or-of metal continuous with conductors 6 and l as shown in .The shaft 8 is rotatably supported on enclosure l by means of bushing I0. Adjustable collar H1 and spring washer I2 serve to maintain the bridge .8 and attached conductors B and l in the proper vertical position. The conductors 6, and

'l are made slightly less in vertical length than" theair gaps between the ends oi'conductors 2-.Ld and 3-5 so that when the shaft .9 is rotated counterclockwise from the position showncoriductors 6 and l occupy the greater-part of-the space between the ends .of conductors 2- 4 and 3-5,, respectively,thus ;re.ducing-the eilective air gaps between these conductors toa minimum.

In order to increase the maximum capacitance obtainable between conductorst-A and between conductors 35, cylindrical shells I3 and M are attached to conductorsdand l, respectively and extend substantially for the full height of the cavity so that the capacitanoes between conductors 24 and shell l3 and between conductors 35 and shell [4 are in parallel with and add to :the 'corresponding gap capacities. 'Theminimum air gaps between the shells l3 and I4 and the condnctorsfi l and 3+5, respectively, may be conveniently fixed by making the conductors 6 and l slightly larger in diameter than conductors ,2 throughiS by the required amount.

The extreme angular position of shaft 9 the counterclockwise direction is that in which.

the conductors =6 and l. are axially aligned 'with conductors :2-4 and 3-.--5, respectively, and the extreme H position in the ieigekwise'diregfiqn is The conductors may 3 that shown in Figs. 1 and 2. The rotation of shaft 9 is kept within these limits by means of pin l5, stop It and a second similar stop not shown in the drawing but located 90 counterclockwise from stop l6.

Input and output coupling to the cavity is provided by loops l1 and I8. Probes may be employed instead of loops if desired. In event the transmission means employed are wave guides, any suitable coupling device, such as an iris, may be used between the wave guide and the cavity.

As already stated, when the shaft 9 is in its extreme counterclockwise position the conductors 8 and 1 are located directly between and in axial alignment with conductors 2-4 and 35, respectively. This position provides the maximum electrical capacity or charge storing facility in the cavity. The magnitude of the capacity is proportional to the end areas of cylindrical conductors 2 through 1 and the areas of shields l3 and I4, and inversely proportional to the length of the air gaps formed between adjacent cylindrical conductors and between the cylindrical conductors and shields i3 and I4. Current paths for periodic equalization of the charge of these capacitances are provided around the boundaries of the cavity. When the conductors 6 and 1 are in the above described position giving maximum capacitance, the inductance of the cavity is also at a maximum value. This is because there is a minimum blocking of the magnetic field area by conductors 6 and 'l and shields l3 and M in this position. Therefore, in the extreme counterclockwise position of shaft 9 the cavity has its lowest resonant frequency.

As the shaft 9 is rotated in a clockwise direction from the above position the capacity becomes continuously less due to the movement of conductors 6 and I from between conductors 2-4 and 35, respectively, and the movement of shields l3 and I4 away from conductors 2-4 and 3-5, respectively. At the same time the inductance also becomes continuously less due to the increasing restriction of the magnetic field area by conductors 6 and l and shields l3 and M. The resonant frequency of the cavity therefore increases with clockwise rotation until, after rotation through 90 to the position shown in Figs. 1 and 2, the capacity and inductance of the cavity have their minimum values and the resonant frequency of the cavity has its highest value.

The tunable cavity shown in Fig. l is capable of wide modification. Figs. 4 and 5 show a modification in which the cavity enclosure I has a rectangular channel extending around its side wall large enough to receive the conductors 6 and I. This construction makes the shields l3 and M of Fig. 1 unnecessary as the conductors 6 and I alone are capable of a high degree of magnetic field area restriction. This modification has the advantage that the shaft 9 and conductors 6 and I may be rotated through 360. The modification of Fig. 3 may be used in Figs. 4 and 5 if desired.

Figs. 6 and '7 show another tunable cavity using the principles of Fig. 1. In this modification the cavity enclosure I" has an elliptical shape. Also, the conductors 2 and 3 of Figs. 1 and 2 are replaced by a single elliptically shaped conductor 20, and located directly beneath conductor 20 is a similar conductor 2| which replaces conductors 4 and 5 of Figs. 1 and 2. Further, a conductor 22 of the same shape as conductors 20 and 2| is used in place of conductors 6 and l of Figs. 1 and 2. Conductors 20, 2| and 22 are hollowed out at the center in orderto reduce the minimum capacity to a low value. As in the case of Figs. 1 and 2, shields l3 and M are used to raise the maximum capacity and to assist in restricting the magnetic field area. In order to provide for an air gap between shields I3 and I4 and conductors 20 and 2|, conductor 22 may be made slightly larger than conductors 20 and 2 I.

The above are not all of the modifications of the tuner possible. Considerable variation may be had in the size, shape and number of conductors in the cavity without departing from the principles of the invention.

I claim:

1. A tuning device comprising metallic means forming an oblong resonant cavity having parallelly arranged upper and lower inner surfaces; conductive means extending from opposite position-s on said upper and lower surfaces and forming oppositely disposed relatively widely spaced electrodes, each of said electrodes being centered relative to the longitudinal axis of said cavity; a conductor having a length slightly less than the transverse dimension of said cavity, a thickness slightly less than the space between said oppositely disposed electrodes and a width commensurate with the cross-sectional dimensions of said electrodes; means for supporting said conductor within said cavity and for moving said conductor to any position between and includin two extreme positions, one of said extreme positions being that in which the longitudinal axisof said conductor is parallel to the longitudinal axis of said cavity and said conductor is positioned between said oppositely disposed electrodes, and the other of said extreme positions allel planar upper and lower inner surfaces, a-

pair of condensers having relatively wide air gaps, each of said condensers being composed of a pair of conductors extending toward each other from opposite points on said upper and lower surfaces, said condensers being positioned along the longitudinal axis of said cavity within a distance substantially equal to the width of said cavity, an oblong conductor having a thickness slightly less than the width of said air gaps and a length slightly less than the width of said cavity, means vertically positioning and pivoting said oblong conductor at its center at a point midway between said condensers and midway of the width of the said cavity so that when the longitudinal axis of said oblong conductor is in the direction of the longitudinal axis of said cavity said oblong conductor substantially fills said air gaps and when in a direction transverse to the longitudinal axis of said cavity said oblong conductor blocks a large portion of the transverse cross-sectional area of said cavity, means for rotating said oblong conductor between its transverse and longitudinal positions to vary the resonant frequency of said tuning device, and means for coupling input and output circuits to said cavity.

3. Apparatus as claimed in claim 2 in which shields having heights slightly less than the distance between said upper and lower surfaces of said cavity are attached to the ends-of said oblong conductor to provide more complete blockmg of the transverse cross-sectional area of said cavity in the transverse position of said oblong conductor and to increase the capacity of said condensers in the longitudinal position of said oblong conductor.

4. A tuning device comprising conductive means enclosing an oblong cavity having parallel planar upper and lower inner surfaces and a wall at right angles to said surfaces, a pair of condensers having relatively wide air gaps, each of said condensers being composed of a pair of conductors extending toward each other from opposite points on said upper and lower surfaces, said condensers being positioned along the longitudinal axis of said cavity and having a maximum separation greater than the transverse distance between the walls of said cavity, an oblong conductor having a thickness slightly less than the width of said air gaps and a length substantially equal to said maximum separation of said condensers, means vertically positioning and pivoting said oblong conductor at its center at a point midway between said condensers on said longitudinal axis so that when the longitudinal axis of said oblong conductor is in the direction of the longitudinal axis of said cavity said oblong conductor substantially fills said air gaps, a channel extending completely around the wall of said cavity of substantially the same width as said air gaps and of sufficient depth to permit rotation of said oblong conductor to a transverse position, means for rotating said oblong conductor between its transverse and longitudinal positions for adjusting the resonant frequency of said tuning device, and means for coupling input and output circuits to said cavity.

5. A tuning device comprising conductive means enclosing a cavity having parallel planar upper and lower inner surfaces and a wall having a channel extending completely therearound, a pair of condensers having air gaps equal to the width of said channel, each of said condensers being composed of a pair of conductors extending toward each other from opposite points on said upper and lower surfaces, said condensers being positioned along the longitudinal axis of said cavity, an oblong conductor having a thickness slightly less than the width of said channel and said air gaps and a length substantially equal to the maximum spacing of said condensers along said longitudinal axis, means pivoting said oblong conductor at its center at a point midway between said condensers on said longitudinal axis so that when the longitudinal axis of said oblong conductor is in the direction of the longitudinal axis of said cavity said oblong conductor substantially fills said air gaps, said channel being only deep enough to permit rotation of said oblong conductor to a position transverse to the longitudinal axis of said cavity, means for rotating said oblong conductor between its transverse and longitudinal positions to vary the tuning of said device, and means for coupling input and output circuits to said cavity.

6. A tuning device comprising conductive means enclosing a cavity bounded by parallel planar upper and lower surfaces and a wall perpendicular to said surfaces, a condenser of relatively wide air gap composed of two stationary conductors of oblong cross-section extending toward each other from said upper and lower surfaces, said oblong conductors being positioned with their longitudinal axes in alignment with the longitudinal axis of said cavity, a movable oblong conductor of length slightly less than the width of said cavity and having a thickness slightly less than said air gap, means positioning said movable conductor between said stationary conductors and pivoting said movable conductor at its center about an axis through the center of said stationary conductors whereby said movable conductor may be rotated from a position in which its longitudinal axis is in alignment with the longitudinal axis of said cavity to a position in which its longitudinal axis is transverse to the longitudinal axis of said cavity, said movable conductor serving to increase the capacity of said condenser to its maximum value in its longitudinal position and to restrict the area for magnetic field lines to a minimum in its transverse position, means for rotatably, moving said movable conductor between its transverse and longitudinal positions for adjusting the resonant frequency of said tuning device, and means for coupling input and output circuits to said cavity.

7. Apparatus as claimed in claim 6 in which the oppositely disposed surfaces of said movable conductor and said stationary conductors are hollowed out about their centers to reduce the capacity of said condenser to a low value when said movable conductor is in its transverse position, and in which shields having heights slightly less than the distance between said upper and lower surfaces are attached to the end portions of said movable conductor to further restrict the area for magnetic field lines in the transverse position of said movable conductor and to increase the maximum capacity of said condenser in the longitudinal position of said movable conductor.

HARRY E. S. STOCKMAN'.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,227,372 Webster et a1 Dec. 31, 1940 2,367,681 Karplus et a1 Jan. 23, 1945 2,471,705 Schmitt May 31, 1949 

